1. Field of the Invention
This application relates to an adapter pan for transferring dry chemicals to and from a storage container, such as a railroad truck, ship or storage tank in a related system and method. The invention is particularly suitable for use with chemicals which form hydrates, in particular soda ash, which can contain larger particles which are difficult to handle.
2. Description of Related Art
Various means have been described for transferring dry materials out of containers. For example, U.S. Pat. No. 3,512,842 describes a method for unloading railroad car, in which a slurry is formed inside the railroad car and then is pumped out. Such a process has numerous drawbacks, however, including the risk of overflowing or foaming within the car; the need for specialized railroad cars adapted for use in the slurrying process; the possibility of corrosive solutions being formed and damaging the railroad car; problems with residual moisture causing caking in subsequent shipments; and the formation of hard, slowly dissolving lumps when liquid is added to a large quantity of solid. A similar approach is described in U.S. Pat. No. 4,189,262.
Eductors have been used and are still used to transfer dry chemicals as a slurry, solution or solid. For example, liquid driven eductors have been used to slurry dry polymers and activated carbon in the water treatment industry and to transfer fly ash in the electric power industry. Also air, steam, and liquid driven eductors have been used for transfer of solids. However, problems are known to exist with eductor-based handling systems.
For example, air driven eductors require a high power input and air flow per unit mass of solid conveyed resulting in high energy costs and higher capital cost for dust collection equipment. Steam driven eductors are used to create a vacuum for pneumatic conveying of dry solids to a solid-liquid mixing apparatus. The systems using steam driven eductors which are known to the inventors require a large amount of support equipment including a barometric leg for condensing the steam with modifications for solid-liquid mixing, and a large steam supply. Since the solid is conveyed by vacuum, the steam driven eductor system is limited by economics to installations where it can be located near, e.g. within a few hundred feet of, the container of dry chemical.
Liquid driven eductors do not require large volumes of air or steam and can be used to transfer dry chemicals from a container, such as a railroad car, forming a solution or slurry of the chemical in the liquid carrier medium. Liquid driven eductors are known to be successfully used to prepare dilute solutions of polymer in water as well as to transfer insoluble materials, e.g. activated carbon, to storage as a slurry.
Commonly assigned U.S. Pat. No. 4,884,925, discloses a apparatus and method for transfer and slurrying or dissolving hydratable dry bulk chemicals hereby incorporated by reference.
Dry bulk material is brought in a storage container, such as a railroad car, and is discharged by gravity to an adapter pan immediately beneath the railroad car. Such pans as are typically used are flat pans open along at least one transverse side and the top. The dry material falls from the railroad car into the pan and is sucked by a flexible hose communicating to an eductor into a hydrator hopper. Such pans have raised environmental concerns regarding dust from the open pan contaminating the environment.
The disclosed hydrator has a sealed solvation hopper positioned between a liquid driven eductor and a fitting for connection to a storage container such as a railroad car. At the inlet end of the solvation hopper is a chemical inlet pipe which connects the interior to the exterior of the hopper. Surrounding the inlet pipe are a plurality of nozzles for introduction of solvation liquid into the hopper. The nozzles are disposed such that the solvation liquid washes the interior surface of the hopper to prevent plugging by hydrates (solvates) which may be formed. The outlet end of the hopper is connected to a suction opening of the liquid driven eductor.
In operation, liquid flowing through the eductor creates a suction and draws dry chemical out of the storage container and into the hopper. In the hopper, solvation liquid is supplied through the nozzles to wet the dry chemicals and to wash the surfaces of the hopper, pushing the wetted material toward the outlet end of the hopper. At the outlet end of the hopper, the wetted material is sucked out of the eductor where it is combined with the flow of eductor liquid. The material leaving the eductor is recovered and sent to storage or directly for processing. The process and apparatus are particularly useful for handling soda ash.
A technical bulletin entitled Soda Ash/Technical/Handling, published by the General Chemical Corporation, 1988 reviews the handling of soda ash. This manual discloses the unloading of soda ash beginning at page 24 where various means to unload soda ash are disclosed. One approach to dust during unloading is to use a flexible shroud between an outlet of a storage car and a conveyor. The soda ash falls by gravity from the outlet of the car through the shrouds and directly into the conveyor.
However, certain railroad cars have large outlet openings that require flat pans to be attached underneath and the opening put into communication with the inlet of the pan. The soda ash falls directly into the pan. In these operations the pans have open sides and the soda ash simply falls out of the open sides onto the surrounding ground or is vacuumed from the open sides. The General Chemical bulletin discloses that certain railroad cars are adapted for direct attachment to pneumatic hoses whereby the soda ash can be vacuum transferred directly from the car.
While improvements have been made in the design and apparatus of unloading bulk soda ash, there are still a large number of railroad cars which are designed with outlets which fit broad, flat pans. It is desirable to be able to continue to use such railroad cars.